The present invention relates to an injection start advancer for a fuel injection pump assembly of the fuel distribution type, and more particularly to an injection start advancer for obtaining an injection starting angle related to the temperature at which fuel injection is started, using a heat-sensitive device housing a heat-sensitive material which is contractable and expandable according to ambient temperature.
FIG. 1 of the accompanying drawings illustrates a conventional injection start advancer for use with an internal combustion engine. A shaft 2 extends through a housing 1 of a fuel injection pump assembly, and a lever 3 is fixed to the inner end of the shaft 2 within the housing 1. A ball pin 3A is angularly movably mounted on the tip end of the lever 3. The housing 1 accommodates therein a roller holder 6 supporting rollers 16 for controlling the timing of axial displacement of a plunger 5 rotatable with a driver shaft 4 of the fuel injection pump assembly, the roller holder 6 having a recess 7 in which the ball pin 3A is inserted. Levers 8, 9 are secured to an outer portion of the shaft 2 which extends outside of the housing 1. The lever 8 is coupled to a spring 10 that normally urges the roller holder 6 in a direction to advance fuel injection. A heat-sensitive device 13 comprises a container 12 housing a heat-sensitive material 12A such for example as wax pellets which is contractable and expandable according to ambient temperature and a movable member 12B having one end held against the heat-sensitive material 12A. The other end of the movable member 12B is fixed to one end of a rod member 11 with its other end engaging the distal end of the lever 9. A pipe (not shown) for passing an engine coolant therethrough is wound around the heat-sensitive device 13.
When the temperature of the engine coolant is higher than a preset temperature, the movable member 12B pushes the end of the rod member 11 to cause the lever 9 to turn the shaft 2 clockwise in FIG. 1, thus positioning the ball pin 3A out of engagement with a lower edge of the recess 7.
At the time of starting the engine from a cold condition, the heat-sensitive material 12A is contracted, allowing the shaft 2 to turn counterclockwise under the resiliency of the spring 10 until the movable member 12B is caused by the rod member 11 to abut against the heat-sensitive material 12A. The ball pin 3A now engages the lower edge of the recess 7 to move the roller holder 6 in the fuel injection advancing direction. Thus, an injection starting angle corresponding to the temperature at the time of starting the engine is obtained.
With the aforesaid conventional injection start advancer, however, if the spring 10 were so strong as to be able to advance the fuel injection timing or increase the injection starting angle as the ambient temperature is lowered, then the heat-sensitive material 12A would be subject to a strong force normally tending to compress the same, resulting in a durability problem of the heat-sensitive material 12A. To avoid this drawback, it has been customary to utilize the difference between the frictional force between the rollers 16 and shafts supporting them at the time the fuel injection pump assembly is rotated and the frictional force between the rollers 16 and their shafts at the time the fuel injection pump assembly is stopped, and to set the force of the spring 10 such that the spring 10 cannot turn the roller holder 6 when the pump assembly is at rest, while the spring 10 can turn the roller holder 6 when the pump assembly is rotated. This can reduce the force acting on the heat-sensitive material 12A during operation of the fuel injection pump assembly, with the consequence that the durability of the heat-sensitive material 12A is increased.
With the aforesaid spring force setting, when the engine is at rest, the heat-sensitive material 12A is contracted without being subjected to the force of the spring 10 as the ambient temperaure descreases. In the absence of any pressure on the heat-sensitive material 12A, it has different temperaure-dependent rates of contraction and expansion, resulting in variations in the fuel injection starting angle that is determined by the position of the distal end of the movable member 12B which engages the rod member 11.